Compound semiconductors are used in various fields such as high-speed electron devices exemplified by high frequency devices, optical devices exemplified by light emitting and light receiving devices, and the like. High-performance devices are in practical use. In order to fabricate high-quality devices, it is generally necessary to prepare a high-quality substrate crystal. However, crystal substrates of compound semiconductors have small diameters, (if it is) compared with silicon substrate which have large diameter. And then, processes for fabricating semiconductors using such substrates are prone to having poor mass-productivity.